1. Field of the Invention
This invention relates to radio integrated circuit (IC) card systems in which power consumption is reduced.
2. Description of the Related Art
Nowadays, research on various types of systems utilizing IC cards is in progress.
It is anticipated that IC cards will be applied to various fields because they include both a mass storage unit and a central processing unit (CPU) for processing data stored in the storage unit, thereby differing from magnetic cards.
At present, IC card systems are classified into a contact IC card system and a radio IC card system (non-contact IC card system).
FIG. 11A shows a block diagram of a contact IC card system.
According to this contact IC card system, transmission or reception of data is performed between an IC card system 100 and a reader/writer unit 101 via connectors 102 and 103.
Since the IC card system 100 and the reader/writer unit 101 are connected by the connectors 102 and 103, a CPU 104 in the IC card 100 can be supplied with power through the connectors 102 and 103.
FIG. 11B shows a block diagram of a conventional radio IC card system.
According to this radio IC card system, transmission or reception of data is performed by radio between an IC card 200 and a reader/writer unit 201 via a transmitter/receiver unit 202. Since this system is radio-operated, the IC card 200 cannot be supplied with power from the reader/writer unit 201. Consequently, the IC card 200 needs a built-in battery 204 to supply power to the transmitter/receiver unit 202 and the CPU 205.
Although the radio IC card system has a more complicated structure than the contact IC card system, transmission or reception of data can be performed over a distance between the IC card 200 and the reader/writer unit 201. Thus, the radio IC card system can be applied to a wide range of fields such as transportation, distribution, and factory automation. For example, by using radio IC cards disposed in automobiles and reader/writer units disposed in tollgates, the identification code of each automobile and the tollgate by which the automobile has passed can be recorded without stopping the automobile at the tollgate because transmission or reception of data can be performed between the IC card and the reader/writer unit. Afterward, the toll is collected online from the bank account specified by the identification code.
A problem associated with the above-described radio IC card system is power consumption while the transmitter/receiver unit is in standby mode.
In other words, to activate the transmitter/receiver unit 202 in the IC card 200 by radio, the transmitter/receiver unit 202 needs to always be in a condition capable of receiving radio waves. For this purpose, the active state of the transmitter/receiver unit 202 must always be maintained.
However, maintaining the active state of the transmitter/receiver unit 202 as always active increases power consumption of the unit 202, and as shown in FIG. 11B, activation of the transmitter/receiver unit 202 by the battery 204 severely shortens the life of the battery 204 due to power consumption by the transmitter/receiver unit 202.
One possible solution to the above problem is to provide a switch between the transmitter/receiver unit 202 and the battery 204 so that the switch is activated only when the IC card is used.
However, the IC card is thin by nature, and is weak against externally applied force, thus, it is not preferable to use a switch-like mechanical member mounted to the IC card, because this would make the IC card less durable.
In addition, compared with the contact IC card system, the radio IC card system has an advantage in that the IC card functions without connection to the connector of the reader/writer unit, in other words, it is automatically operated without being touched by the user, but merely by being possessed by the user. This advantage is lost in the IC card if the power switch must be manually turned on for each use.